Methods and systems for operating HVAC systems in low load conditions

ABSTRACT

A system comprising a compressor, a first valve coupled to the compressor and coupled to a first coil, a first expansion valve coupled to the first coil, a second coil, and a second expansion valve. The second expansion valve coupled to a third coil, a second valve coupled to the compressor and the third coil. A controller operable to operate the first valve, the first expansion valve, the second expansion valve, and the second valve. The second coil is coupled to the compressor and the refrigerant flows from the second coil to the compressor.

RELATED APPLICATION

This application claims benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application Ser. No. 62/084,492, titled “HVAC SystemOperating Schemes in Extra Low Load Conditions,” filed Nov. 25, 2014.This application is incorporated herein by reference.

TECHNICAL FIELD

This application is directed, in general, to HVAC (heating, ventilating,and air conditioning) systems, and more specifically to HVAC systems foroperating in low load conditions.

BACKGROUND

HVAC systems often need to be able to operate across a range of systemloads. Present HVAC systems operate ineffectively or not at all in lowload conditions. Thus, methods and systems are needed for HVAC systemsto operate effectively in low load conditions.

SUMMARY OF THE DISCLOSURE

A system comprising a compressor operable to compress refrigerant, afirst valve coupled to the compressor and coupled to a first coil, afirst expansion valve coupled to the first coil, a second coil, and asecond expansion valve is disclosed. In the system, the second expansionvalve is further coupled to a third coil, a second valve is coupled tothe compressor and the third coil. Further, a controller operable to, inresponse to receiving a cooling demand that is below a threshold coolingdemand, operate the first valve to direct the refrigerant from thecompressor into the first coil, operate the first expansion valve todirect a first amount of the refrigerant from the first coil to thesecond coil and a second amount of the refrigerant from the first coilto the second expansion valve, operate the second expansion valve todirect the second amount of the refrigerant to the third coil, andoperate the second valve to direct the second amount of refrigerant fromthe third coil to the compressor is disclosed. In the system, the secondcoil is coupled to the compressor and the first amount of therefrigerant flows from the second coil to the compressor.

The present embodiment presents several technical advantages. First, thepresent embodiment discloses an HVAC system that operates efficiently inboth low load conditions and regular load conditions. Second, thepresent embodiment can effectively cool or heat an environment in low orregular load conditions. Third, the present embodiment providesflexibility for controlling the climate of an environment using anintelligent controller.

Certain embodiments of the present disclosure may include some, all, ornone of these advantages. One or more other technical advantages may bereadily apparent to those skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and theadvantages thereof, reference is now made to the following DetailedDescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of an outdoor section of a VRF system;

FIG. 2 is a flow chart of a method of control of metering valves by asystem controller;

FIG. 3 is a refrigerant flow diagram during operation of a VRF system inlow cooling mode; and

FIG. 4 is a refrigerant flow diagram during operation of a VRF system inlow heating mode.

DETAILED DESCRIPTION

Variable Refrigerant Flow (VRF) systems are a type of HVAC systemconsisting of multiple indoor units and one or more outdoor units. VRFsystems may be configured for heat pump operation, capable of providingeither heating or cooling supply air to a conditioned space through useof a reversing valve to change the direction of refrigerant flow throughVRF system components.

Each indoor unit of a VRF system comprises an indoor coil and isconfigured to condition supply air for delivery to a specific zone ofconditioned space within a building. Each indoor unit of a VRF systemmay be paired with one or more outdoor units, forming one or morerefrigerant flow circuits. Each outdoor unit may comprise one or moreoutdoor coils. Each of the multiple indoor units of a VRF systemoperates to provide conditioned air to a specific, and separate, zonewithin a building. Each indoor unit may operate independently of theother indoor units, such that some, none, or all of the indoor units maybe in operation simultaneously.

A particular type of VRF system, a 3-pipe VRF system, has the additionalcapability of operating one or more indoor units to provide cooling airwhile simultaneously operating one or more other indoor units to provideheating air. When operating under simultaneous heating and coolingdemand conditions, the VRF system uses routes refrigerant flow throughthe system so that indoor coils in heating mode function as a condenserunit providing sub-cooled liquid refrigerant to indoor coils operatingin cooling mode. In this manner, the individual heating and coolingdemands of multiple zones within a building having a 3-pipe VRF systemmay be accommodated.

VRF systems are designed to operate efficiently in part load, or lessthan full capacity, conditions through adjustment of the overall heatingor cooling capacity of the system to match the combined demand of all ofthe indoor zones. For example, in a VRF system having two indoor unitsproviding conditioned supply air to two distinct zones of conditionedspace within a building, the first zone may be operating at full loadcooling demand while there may be no demand for conditioned supply airin the second zone. Under such conditions, the total system demand maybe equal to approximately half of the system's full load coolingcapacity. To operate more efficiently, the VRF system may respond tosuch conditions by retarding system cooling capacity to match thecombined demand experienced among the several indoor zones.

The VRF system may match the cumulative demand of the conditioned spaceswithin a building through adjustment of the flow rate of refrigerantcirculated through the system components. The refrigerant flow rate maybe adjusted through use of a multispeed, or variable speed, compressor.Such compressors are commonly implemented with an inverter, orvariable-speed, drive to vary the compressor speed through variation ofthe frequency and voltage of power applied to the compressor motor.

Unfortunately, control of VRF system capacity in this way is limited bythe operating range of the variable, or multispeed, compressor.Commonly, inverter equipped variable speed compressors are incapable ofoperating at speeds corresponding to extra low system capacity ranges.For example, a particular variable speed compressor implemented with aninverter may be limited to an operating RPM range of between 20% and100% of full speed operation. In a VRF system implemented with such acompressor, system demands of below approximately 20% may not be met bythe VRF system since the compressor may not be energized at speeds belowits operating range. Alternatively, the compressor may be energized atits lowest speed setting, causing the VRF system to inefficientlyprovide conditioned air at a capacity higher than demanded. Operation inthis manner also leads to rapid power cycling of the compressor duringextra low load operation, reducing the life of the compressor.

In VRF systems, in particular, extra low demand for conditioned supplyair is common, as one or more zones may experience a low, or partialload, demand for conditioned supply air while other zones maysimultaneously place no demand for conditioned supply air on the system.Under such conditions, the extra low cumulative system demand from allzones may correspond to compressor operation at a speed below theoperational range of the compressor, rendering the system incapable ofcomfortably, efficiently, and reliably accommodating the cooling andheating demands on the VRF system. A need exists for a VRF systemcapable of operation in extra low load conditions. Specifically, a needexists for a VRF system capable of accommodating a greater range ofsystem demand, with the range not limited at its lower end by theoperating capabilities of the system compressor.

In the following discussion, numerous specific details are set forth toprovide a thorough understanding of the present disclosure. However,those skilled in the art will appreciate that the present embodiment maybe practiced without such specific details. Additionally, for the mostpart, details concerning any well-known features and elements have beenomitted inasmuch as such details are not considered necessary to obtaina complete understanding of the present disclosure, and are consideredto be within the understanding of persons of ordinary skill in therelevant art.

Referring to FIG. 1, a block diagram of the outdoor section componentsand piping arrangement of VRF system 1000 according to an embodiment ofthe present embodiment is shown. The VRF system 1000 may be a three pipeVRF unit configured for heat pump operation and comprising a singleoutdoor unit, having two outdoor coils, coupled with one or more indoorunits (not shown). The VRF system 1000 may include a compressor assembly100, two valves 200A and 200B, two outdoor coils 300A and 300B, two fanassemblies 400A and 400B, two metering device 500A and 500B, a reversingvalve 600, a controller 700, and an indoor coil 800.

Although the embodiment shown in FIG. 1 corresponds to simplified systemcomponents and piping for a single refrigerant flow circuit, theapparatus and method described herein may be utilized in multi-stage VRFsystems having multiple refrigerant flow circuits.

In alternative embodiments, VRF system 1000 may include additional,fewer, or different components than those shown in FIG. 1. For example,in an alternative embodiment, VRF system 1000 may be provided with morethan one compressor 100, with more than two valves 200, more than twooutdoor coils 300, more than two fan assemblies 400, with more than twometering devices 500, with more than one reversing valve 600, and/orwith more than one indoor coil 800, and the like. The VRF system 1000may, in alternative embodiments, be provided with additional componentsand associated piping, such as one or more oil separators, one or morecrankcase heaters, one or more check valves, one or more refrigerantaccumulators, one or more pressure and/or temperature sensors, and thelike.

Further, VRF system 1000 components may be located in different sectionsof the VRF 1000 system than shown. For example, some, none, or all ofthe system components such as the compressor 100, the valves 200, themetering devices 500, the reversing valve 600, and the controller 700may be located elsewhere in the VRF system 1000, such as in an indoorsection, for example, and not within the outdoor section.

As shown in FIG. 1, the VRF system 1000 may include a compressorassembly 100 for pumping refrigerant from the low pressure to the highpressure sides of a VRF system 1000. The compressor assembly 100 may beconfigured to pump refrigerant through the VRF system 1000 at a variableflow rate, configured to match VRF system 1000 demand. The compressorassembly 100 may operatively connect to, and receive power and controlsignals from, the system controller 700.

The compressor assembly 100 may comprise a compressor 102 operativelycoupled to a variable speed drive 104 for varying the speed of thecompressor 102. The compressor 102 may be of any type, such as a scrollcompressor, a reciprocating compressor, or the like. Compressor 102 maybe any device for compressing refrigerant.

The variable speed drive 104 may adjust the speed of the compressor 102,varying the flow rate of refrigerant through the compressor 102. Thevariable speed drive 104 may adjust the compressor 102 speed through anysuitable method, such as through frequency modulation of an incomingpower signal, voltage modulation of an incoming power signal, or othersuitable methods. In an alternative embodiment than that shown in FIG.1, the variable speed drive 104 may be an internal component of thecompressor 102 or, alternatively, incorporated within the systemcontroller 700.

The VRF system 1000 may include valves 200A and 200B for routingrefrigerant flow received from compressor assembly 100 through the VRFsystem 1000. As shown in FIG. 1, the valves 200A and 200B may each befour-way valves configured to route refrigerant flow through the valve200 along one of two paths, as desired. The valves 200A and 200B may beany other type of suitable valves. The valves 200A and 200B may beoperatively connected to the system controller 700 for receiving controlsignals setting the position of valves 200A and 200B. In an alternativeembodiment, the valves 200A and 200B may be replaced with a series ofshutoff valves, check valves, or the like, and configured to permitrefrigerant flow along a desired path. As shown in FIG. 1, the valve200A may be paired with the outdoor coil 300A while the valve 200B maybe paired with the outdoor coil 300B. This configuration may allow forrefrigerant flow to be directed from the discharge of the compressorassembly 100 to either, or both, of the outdoor coils 300A and 300B,depending on the heating or cooling demand to which the VRF system 1000is operating in response to.

Returning to FIG. 1, the VRF system 1000 may include outdoor coils 300Aand 300B and indoor coil 800. Outdoor coils 300A and 300B and indoorcoil 800 may allow for heat transfer between VRF system 1000 refrigerantand the outdoor air passing over the outdoor coils 300A and B and indoorcoil 800. In an embodiment, the size, shape, piping configuration,and/or heat transfer capacity of the outdoor coils 300A and 300B andindoor coil 800 may be equal. Alternatively, in an embodiment, one ormore outdoor coils 300 and indoor coil 800 may vary in size, shape,piping configuration, and/or heat transfer capacity from each other.

The VRF system 1000 may include fans 400A and 400B. The fans 400A and400B may induce airflow across the outdoor coils 300A and 300B. The fans400A and 400B may include a plurality of blades that may be rotatedabout a hub in response to a control signal input to a motor. The fans400A and 400B may be configured to operate at different speeds and inone of two directions, as desired, to push air across, or draw airthrough, the outdoor coils 300A and 300B. In some embodiments, one ormore indoor fans may also induce airflow across indoor coil 800.

As shown in FIG. 1, the fan 400A may be paired with the outdoor coil300A while the fan 400B may be paired with the outdoor coil 300B. Inalternative embodiments, more or fewer fans 400 may be provided. Forexample, in an embodiment, a single fan 400 may be provided for inducingairflow across all of the outdoor coils 300. In an alternativeembodiment, each outdoor coil 300 may be paired with multiple fans 400.In such an embodiment, the fans 400 may be controlled by the systemcontroller 700 independently, or in concert.

The fans 400A and 400B may be operably connected to, and may receivecontrol and power signals from, the system controller 700 via a wired orwireless connection. The fans 400A and 400B may be configured forvariable speed operation in response to heating and cooling demand onthe VRF system 1000. The fans 400A and 400B may be operated, forexample, at higher speed to induce more airflow over the outdoor coils300A and 300B to increase the rate of heat transfer between the VRFsystem 1000 refrigerant and the outdoor air to accommodate higherheating or cooling demand on the VRF system 1000. Conversely, the fans400A and 400B may be operated at lower speeds, or, in a furtheralternative, turned off, in response to lesser heating or cooling demandon the VRF system 1000.

The electrical input to the fans 400A and 400B may be a direct current(DC) input or an alternating current (AC) input. The control signal maybe a pulse-width modulated (PWM) signal in which the relative width ofpulses determines the level of power applied to the fans 400A and 400B.The revolutions per minute (RPM) of the fans 400A and 400B may have adirect relationship to the width of PWM pulses. Alternatively, thecontrol signal may be the power applied to the fans 400A and 400B whichmay be switched on and off, with the controller 700 setting theamplitude of the power signal to control the speed of the fans 400A and400B. Alternatively, the speed of the fans 400A and 400B may becontrolled using any suitable methods of fan speed control.

As shown in FIG. 1, the VRF system 1000 may include two metering devices500A and 500B for controlling the rate of refrigerant flow between VRFsystem 1000 components and causing a pressure drop of the refrigerantfluid as part of the vapor compression cycle. Either or both of themetering devices 500A and 500B may be expansion valves. These expansionsvalves may be of any suitable type including electronic expansion valves(EXV). The expansion valves may any valves that regulate the flow of therefrigerant fluid inside VRF system 1000.

In an embodiment, the metering devices 500A and 500B may both be EXVswhich may each be operatively connected to, and receive control signalsfrom, the system controller 700 by a wired or wireless connection. Thesystem controller 700 may control each metering device 500A and 500B,adjusting the size of the opening through the metering devices 500A and500B that refrigerant may flow in response to the heating or coolingdemand on the VRF system 1000 and using sensed refrigerant temperatureand pressure data.

In the embodiment shown, for example, the controller 700 may commandone, or both, metering devices 500A and 500B to the fully open positionduring normal, full load, cooling operation. Similarly, in theembodiment shown, the controller 700 may command one, or both, meteringdevices 500A and 500B to a partially open position, or a closedposition, during partial load cooling operation. Further, in theembodiment shown, for example, the controller 700 may command one, orboth, metering devices 500A and 500B to a fully open, partially open, orfully closed position to adjust the rate of refrigerant flow througheach, or both, metering devices 500 during heating operation.

In an alternative embodiment, one, or both, metering devices 500 may bereplaced with a combination of components configured to perform therefrigerant metering function as described herein, and below. In aparticular embodiment, for example, the metering devices 500A and/or500B functions may be performed by a check valve and a short orifice orTXV arranged in parallel with one another, whereby one, or both, checkvalves may be opened, or closed, to selectively allow refrigerant flowto bypass the short orifices or TXVs in response to specific operatingconditions of the VRF system 1000.

In a VRF system utilizing one or more check valve and TXV, or checkvalve and short orifice, metering device 500 combinations, one or morecheck valves may be in the open position, allowing the refrigerant flowto bypass the corresponding TXV or short orifice components duringnormal cooling operation. In a VRF system utilizing one or more checkvalve and TXV, or check valve and short orifice, metering device 500combinations, one or more check valves may be in the closed position,forcing refrigerant flow through the corresponding TXV or short orificecomponents during heating operation.

The VRF system 1000 may include a reversing valve 600 for setting thedirection of flow of refrigerant in the VRF system in one of twodirections, as desired, and in accordance with any suitable methods ofheat pump operation. The reversing valve 600 may be a four way valve ofany type of suitable valve. The reversing valve 600 may be operativelyconnected to the system controller 700 via a wired or wirelessconnection.

The VRF system 1000 may be provided with a system controller 700 forcontrolling operation of VRF system 1000 components, including thecompressor assembly 100 components, the valves 200A and 200B, the fans400A and 400B, the metering devices 500A and 500B, and the reversingvalve 600, as well as other components comprising the VRF system 1000not shown in FIG. 1. The controller 700 may be connected to the VRFsystem 1000 components via wired or wireless connections. The controller700 may be implemented with hardware, software, or firmware definingmethods of VRF system 1000 control operation. Further, the controller700 may be implemented with logic for VRF system 1000 control duringextra low heating or cooling demand in accordance with the method shownin FIG. 2.

System controller 700 may have an interface 702, processor 704, andmemory 706 for performing the functions of system controller 700. Thesystem controller 700 memory may store VRF system 1000 characteristicsincluding a low heating demand threshold and a low cooling demandthreshold in memory 706. Memory 706 may include any one or a combinationof volatile or non-volatile local or remote devices suitable for storinginformation. For example, memory 706 may include RAM, ROM, flash memory,magnetic storage devices, optical storage devices, network storagedevices, cloud storage devices, solid state devices, or any othersuitable information storage device or a combination of these devices.Memory 706 may store, either permanently or temporarily, data,operational software, other information for system controller 700.Memory 706 may store information in one or more databases, file systems,tree structures, relational databases, any other suitable storagesystem, or any combination thereof. Furthermore, different informationstored in memory 706 may use any of these storage systems. Theinformation stored in memory 706 may be encrypted or unencrypted,compressed or uncompressed, and static or editable. Memory 706 may storeinformation in one or more caches.

Interface 702 may receive and transmit signals and inputs from and tousers, remote sensors, or any other component of VRF system 1000.Interface 702 may also communicate with processor 704 and memory 706.Interface 702 may be any port or connection, real or virtual, includingany suitable hardware and/or software, including protocol conversion anddata processing capabilities, to communicate through a LAN, WAN, orother communication system that allows system controller 700 to exchangeinformation with any user or component of VRF system 1000. For example,interface 702 may be operable to receive temperature information orpressure information from remote temperature and pressure sensors. Atemperature sensor may be any thermometer or other temperature sensingdevice. The temperature sensor may be alcohol based, mercury based orbased on any other suitable material.

Processor 704 may be any electronic circuitry, including, but notlimited to microprocessors, application specific integrated circuits(ASIC), application specific instruction set processor (ASIP), and/orstate machines, that communicatively couples interface 702 and memory706 and controls the operation of system controller 700. In someembodiments, processor 704 may be single core or multi-core having asingle chip containing two or more processing devices. Processor 704 maybe 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture.Processor 704 may comprise an arithmetic logic unit (ALU) for performingarithmetic and logic operations, processor registers that supplyoperands to the ALU and store the results of ALU operations, and acontrol unit that fetches instructions from memory and executes them bydirecting the coordinated operations of the ALU, registers and othercomponents. Processor 704 may include other hardware and software thatoperates to control and process information. Processor 704 may executecomputer-executable program instructions stored in system controller 700memory. Processor 704 may not be limited to a single processing deviceand may encompass multiple processing devices.

Turning now to FIG. 2, the controller 700 may control the VRF system1000 components according to the flowchart shown in FIG. 2. At step 201,the controller 700 may sense extra low demand on the VRF system 1000.The controller 700 may sense extra low demand based on several inputsources to the controller 700, such as data from sensors, user input atthe system controller 700 or thermostat, system component operationalcapabilities, stored data and functions within the controller 700, andthe like.

At step 201, the controller 700 may further determine whether the sensedextra low demand is extra low heating or cooling demand. At step 202,the controller may provide control signals setting the position ofseveral system components, which may include the compressor assembly100, the valves 200, the fans 400, the metering devices 500, and thereversing valve 600 to configure the VRF system for operation to meetthe sensed demand.

At step 202, for example, the controller 700 may respond to sensingextra low cooling demand by providing control signals to the VRF system1000 components as follows: (1) the valves 200A and B may be positionedto route refrigerant flow from the compressor assembly 100 discharge toonly outdoor coil 300A; (2) the metering device 500A may be commanded tothe fully open position; (3) the metering device 500B may be commandedto a partially open position; (4) the fans 400 speeds may be set todesired speeds; (5) the reversing valve 600 may be positioned forcooling operation; and (6) the compressor assembly 100 may be configuredto operate at its lowest speed setting.

With the VRF system 1000 components configured as described, a portionof the refrigerant flow of the VRF system 1000 may be routed through theoutdoor coil 300B to induce an artificial cooling load. The artificialload induced into the VRF system 1000 may increase total VRF system 1000cooling demand to above the cooling capacity corresponding to operationof the compressor assembly 100 at its lowest speed setting.

Alternatively, at step 202, for example, the controller 700 may respondto sensing extra low heating demand by providing control signals to theVRF system 1000 components as follows: (1) the valves 200A and B may bepositioned to allow some refrigerant flow from the compressor assembly100 discharge to flow directly to the outdoor coil 300A, whilepreventing any refrigerant flow from the compressor assembly 100discharge from flowing directly to the outdoor coil 300B; (2) themetering device 500A may be commanded to a partially open position; (3)the metering device 500B may be commanded to a partially open position;(4) the fans 400 speeds may be set to desired speeds; (5) the reversingvalve 600 may be positioned for heating operation; and (6) thecompressor assembly 100 may be configured to operate at its lowest speedsetting.

With the VRF system 1000 components configured as described, a portionof the refrigerant flow of the VRF system 1000 may be routed through theoutdoor coil 300A to induce an artificial heating load. The artificialload induced into the VRF system 1000 may increase total VRF system 1000heating demand to above the cooling capacity corresponding to operationof the compressor assembly 100 at its lowest speed setting.

At step 203, the controller may monitor the VRF system 1000 during extralow heating or cooling operation, varying the VRF system configurationin response to changes in system demand. The controller 700 may, forexample, vary the position of one or both of the metering devices 500 toincrease or reduce the rate of refrigerant flow through one or both ofthe outdoor coils 300. Additionally, or alternatively, the controller700 may increase or decrease the fans 400 speeds to increase or decreasethe heat transfer between the VRF system 1000 refrigerant and ambientoutdoor air in any suitable manner.

Further, at step 203, the controller 700 may sense that the extra lowheating or cooling demand has ceased. If the extra low heating orcooling demand ceases due to a demand increase to above extra lowdemand, the controller may continue to control the VRF system 1000 inaccording to partial load, or full load, operation. The systemcontroller 700 may return to partial load operation by reconfiguring theVRF system 1000 components to remove the artificial heating or coolingload induced during extra low load operation. If the extra low heatingor cooling demand ceases due to a decrease in demand to below athreshold demand, the controller 700 may de-energize the VRF system 1000components to cease all heating or cooling operation.

Turning now to FIG. 3, the VRF system 1000 may operate in response toextra low cooling demand on the VRF system 1000 in accordance with thecontrol method 200 described above. During extra low cooling loadoperation, the refrigerant flow through the VRF system 1000 may followthe path shown by the arrows of FIG. 3, along the piping route shown insolid lines.

The system controller may set the valve 200A position to routerefrigerant from the compressor assembly 100 discharge to the outdoorcoil 300A. The metering device 500A may be set to the fully openposition. The metering device 500B may be set to a partially openposition. In this configuration, the refrigerant may pass throughmetering device 500A, with some of the refrigerant flow continuing tothe indoor sections of the VRF system 1000, including an indoor coil,and some of the refrigerant flow routed through the metering device 500Band through the outdoor coil 300B. The portion of the refrigerant flowpassing through the outdoor coil 300B may then be routed through thevalve 200B to recombine with the portion of the refrigerant flowreturning from the indoor sections of the VRF system 1000. The combinedrefrigerant may then be piped to the suction port of the compressorassembly 100, completing the circuit.

In extra low cooling mode, as described above, the outdoor coil 300A mayfunction as a condenser while the outdoor coil 300B may function as anevaporator. The outdoor coil 300B may be utilized in this manner as adummy, or artificial, load upon the VRF system 1000, with the outdoorcoil 300B absorbing some of the cooling capacity of the refrigerant flowthrough the VRF system 1000. The artificial load of the outdoor coil300B may augment the total VRF system 1000 cooling demand to bring thedemand to above the capacity corresponding to that of the VRF system1000 when operating at the lowest speed setting of the variable speedcompressor assembly 100.

Operation in this manner allows for the VRF system 1000 to meet extralow cooling demand that is below the lowest capacity that may beaccommodated through a reduction of compressor speed, alone.Additionally, the creation of an artificial load on the VRF system 1000allows for continuous operation of the compressor assembly 100 at itslowest speed setting while the VRF system 1000 meets the extra lowcooling demand, without the need for short cycling of the compressorassembly 100 components.

The controller 700 may control the amount of refrigerant coolingcapacity absorbed by the artificial load of the outdoor coil 300Bthrough control of the metering device 500B, for VRF systems 1000 withthe metering device 500B being an EXV. The area of the opening throughthe metering device 500B may be varied by the controller 700 to adjustthe amount of refrigerant flow that passes through the metering device500B and the outdoor coil 300B. The controller 700 may command themetering device 500B towards the fully open position to allow morerefrigerant flow to pass to the outdoor coil 300B to increase theartificial load on the VRF system 1000. Alternatively, the controller700 may command the metering device 500B toward the closed position toreduce the refrigerant flow to the outdoor coil 300B to decrease theartificial load on the VRF system 1000.

The controller 700 may also control the artificial load created throughvarying the speed of one or more of the fans 400B. The controller 700may increase the speed of one or more of the fans 400B to increase theheat transfer between the refrigerant flow through the outdoor coil 300Band the ambient outdoor air, increasing the artificial load on the VRFsystem 1000. The controller 700 may decrease the speed of one or more ofthe fans 400B to decrease the heat transfer between the refrigerant flowthrough the outdoor coil 300B and the ambient outdoor air, reducing theartificial load on the VRF system 1000.

In an embodiment, the controller 700 may be configured to control theartificial load created through variation of the either, or both, theposition of the metering devices 500 and the speed of one or more fans400. Those skilled in the art will appreciate that the controller 700may be configured to position the metering devices 500A and 500B and thevalves 200A and 200B to utilize outdoor coil 300A as an evaporator coilinducing an artificial load into the VRF system 1000.

Turning now to FIG. 4, the VRF system 1000 may operate in response toextra low heating demand on the VRF system 1000 in accordance with thecontrol method described above. During extra low heating load operation,the refrigerant flow through the VRF system 1000 may follow the pathshown by the arrows of FIG. 4, along the piping route shown in solidlines.

The system controller may set the reversing valve 600 position toreverse the flow of refrigerant through the VRF system 1000, routing therefrigerant from the discharge of the compressor assembly 100 to theindoor sections of the VRF system 1000, such as an indoor coil. Thesystem controller 700 may set the valve 200A position to route some ofthe refrigerant from the compressor assembly 100 discharge to theoutdoor coil 300A.

The metering device 500A may be set to a partially open position,limiting the portion of the VRF system 1000 flowing through the outdoorcoil 300A. The metering device 500B may also be set to a partially openposition to control the phase change of the refrigerant flow passingthrough it, in a manner consistent with metering device operation for aheat pump in heating mode. In this configuration, the refrigerant flowfrom the compressor assembly 100 discharge is routed directly to theindoor sections of the VRF system 1000 with a portion of the refrigerantflow routed through the outdoor coil 300A and the metering device 500A.The divergent flow routes may re-combine at the metering device 500B.The total refrigerant flow may then pass through the outdoor coil 300Band may be routed through the valve 200B to the suction port of thecompressor assembly 100, completing the circuit.

In extra low heating mode, as described above, the outdoor coil 300A mayfunction as a condenser while the outdoor coil 300B may function as anevaporator. The outdoor coil 300A may be utilized in this manner as adummy, or artificial, load upon the VRF system 1000, with the outdoorcoil 300A absorbing some of the heating capacity of the refrigerant flowthrough the VRF system 1000. The artificial load of the outdoor coil300A may augment the total VRF system 1000 heating demand to bring thedemand to above the capacity corresponding to that of the VRF system1000 when operating at the lowest speed setting of the variable speedcompressor assembly 100.

Operation in this manner allows for the VRF system 1000 to meet extralow heating demand that is below the lowest capacity that may beaccommodated through a reduction of compressor speed, alone.Additionally, the creation of an artificial load on the VRF system 1000allows for continuous operation of the compressor assembly 100 at itslowest speed setting while the VRF system 1000 meets the extra lowheating demand, without the need for short cycling of the compressorassembly 100 components.

The controller 700 may control the amount of refrigerant heatingcapacity absorbed by the artificial load induced by the outdoor coil300A through control of the metering device 500A, for VRF systems 1000with the metering device 500A being an EXV. The area of the openingthrough the metering device 500A may be varied by the controller 700 toadjust the amount of refrigerant flow that passes through the meteringdevice 500A. The controller 700 may command the metering device 500Atowards the fully open position to allow more refrigerant flow topassing through the outdoor coil 300A to recombine with the refrigerantflow returning from the indoor sections of VRF system 1000 to increasethe artificial load on the VRF system 1000. Alternatively, thecontroller 700 may command the metering device 500A toward the closedposition to reduce the refrigerant flow from the outdoor coil 300A thatmay recombine with the refrigerant returning from the indoor sections ofthe VRF system 1000 to decrease the artificial load on the VRF system1000.

The controller 700 may also control the artificial load created throughvarying the speed of one or more of the fans 400A. The controller 700may increase the speed of one or more of the fans 400A to increase theheat transfer between the refrigerant flow through the outdoor coil 300Aand the ambient outdoor air, increasing the artificial load on the VRFsystem 1000. The controller 700 may decrease the speed of one or more ofthe fans 400A to decrease the heat transfer between the refrigerant flowthrough the outdoor coil 300A and the ambient outdoor air, reducing theartificial load on the VRF system 1000.

In an embodiment, the controller 700 may be configured to control theartificial load created through variation of the either, or both, theposition of the metering devices 500 and the speed of one or more fans400. Those skilled in the art will appreciate that the controller 700may be configured to position the metering devices 500A and 500B and thevalves 200A and 200B to utilize outdoor coil 300B as a condenser coilinducing an artificial load into the VRF system 1000 during extra lowheating operation.

Modifications, additions, or omissions may be made to the systems,apparatuses, and processes described herein without departing from thescope of the disclosure. The components of the systems and apparatusesmay be integrated or separated. Moreover, the operations of the systemsand apparatuses may be performed by more, fewer, or other components.The methods may include more, fewer, or other steps. Additionally, stepsmay be performed in any suitable order. Additionally, operations of thesystems and apparatuses may be performed using any suitable logic. Asused in this document, “each” refers to each member of a set or eachmember of a subset of a set.

Although several embodiments have been illustrated and described indetail, it will be recognized that substitutions and alterations arepossible without departing from the spirit and scope of the presentdisclosure, as defined by the appended claims. To aid the Patent Office,and any readers of any patent issued on this application in interpretingthe claims appended hereto, applicants do not intend any of the appendedclaims to invoke 35 U.S.C. § 112(f) as it exists on the date of filinghereof unless the words “means for” or “step for” are explicitly used inthe particular claim.

The invention claimed is:
 1. A system comprising: a compressor operableto compress refrigerant; a first valve positioned between and coupled tothe compressor and a first coil; a first expansion valve positionedbetween and coupled to the first coil and a second coil, wherein thesecond coil is further coupled to the compressor; a second expansionvalve positioned between and coupled to the first expansion valve andthird coil; a second valve positioned between and coupled to thecompressor and the third coil; a controller operable to, in response toreceiving a cooling demand that is below a threshold cooling demand,induce an artificial cooling demand by: operating the first valve todirect the refrigerant discharged from the compressor into only thefirst coil; operating the first expansion valve to direct a first amountof the refrigerant from the first coil to the second coil and a secondamount of the refrigerant from the first coil to the second expansionvalve; operating the second expansion valve to direct the second amountof the refrigerant to the third coil; and operating the second valve todirect the second amount of refrigerant from the third coil to thecompressor; wherein the second coil is coupled to the compressor and thefirst amount of the refrigerant flows from the second coil back to thecompressor.
 2. The system of claim 1, further comprising one or morefans are coupled to the controller wherein the one or more fans areoperable to blow ambient air across the first coil or the third coil andwherein the controller is operable to regulate the speed of the one ormore fans based in part on the cooling demand.
 3. The system of claim 1,wherein the second coil is placed inside a building and the first coiland the third coil are placed outside the building.
 4. The system ofclaim 1, wherein the controller is operable to regulate the speed of thecompressor by using a variable speed drive coupled to the compressor. 5.The system of claim 1, wherein the controller is operable to determineif a cooling demand is below a threshold cooling demand based on astored cooling demand in a controller memory.
 6. The system of claim 1,wherein the first valve and the second valve are both four-way valves.7. The system of claim 1, wherein the controller is wirelessly coupledto the compressor.